Automotive vehicles have implemented heat pump type air conditioning and heating systems to provide both cooling and heating to the passenger compartment of the vehicles. Such systems may include an outside heat exchanger, an inside heat exchanger located inside an HVAC module, a compressor, and a four-way, reversing valve for changing the direction of the refrigerant flow to and from the compressor when switching from cooling mode to heating mode, or vice versa. In some systems, there may be two inside heat exchangers located inside the HVAC module where they may be configured to selectively operate in parallel and/or in series. The systems also may include other devices as well, including, but not limited to, metering devices, valves, fans, and blowers.
In cooling mode, the inside heat exchanger(s) acts as a heat absorber, or an evaporator, and the outside heat exchanger acts as a heat radiator, or a condenser. The refrigerant flows from the compressor through the outside heat exchanger, into a metering device, such as a thermal expansion valve (TXV), and then through the inside heat exchanger(s). Heat is extracted from the air blown across the inside heat exchanger(s), thereby providing cooled air to the passenger compartment.
In heating mode, the outside heat exchanger acts as the evaporator, and the inside heat exchanger(s) acts as the condenser. The reversing valve reverses the flow of the refrigerant such that it flows from the compressor through the inside heat exchanger(s), into a metering device, and then through the outside heat exchanger. Heat from the refrigerant is rejected by the air blown across the inside heat exchanger(s), thereby providing heat to the passenger compartment.
When the inside heat exchanger(s) is used first as an evaporator, and subsequently is used as a condenser, as when switching from a cooling mode to a heating mode, flash fog may occur within the passenger compartment. This occurs when condensate left on the inside heat exchanger(s) from the cooling operation rapidly evaporates or flashes when the inside heat exchanger(s) becomes warm or hot. Some vehicular heat pump systems may implement and run an HVAC module blower in an attempt to dry off the condensate when the vehicle is shut off.